1. Field of the Invention
This invention relates to control systems and, in particular, to programmable control systems with means for limiting access to a plurality of control levels for controlling a cooking system. Moreover, an embodiment of the invention is directed to a programmable control system capable of controlling a three-well open fryer. A further embodiment of the invention includes three levels of access to the control system: an operator's control level, a manager's control level, and a supervisor's or diagnostic technician's control level.
2. Description of the Related Art
It is known that cooking systems, such as deep fat fryers, may be equipped with means for restricting access to programmable controls. These control systems provide a variety of access means, such as numerical access codes, see, e.g., U.S. Pat. No. 4,636,949 to Limgabaugh and U.S. Pat. No. 4,431,159 to Waugh; access keys, see, e.g., U.S. Pat. No. 4,913,038 to Burkett et al.; and the sequential operation of data entry switches, see, e.g., U.S. Pat. No. 4,858,119 to Waugh et al. Each of these references, however, appears only to disclose means for limiting access to a single level of the control program. Other related systems have also attempted to ensure the reliable operation of the control system by providing activation means which only engage the cooking system or start a cooking cycle when the activation means, e.g., the switch, have been depressed for a predetermined period, such as those disclosed in U.S. Pat. No. 5,097,113 to Aoyama and U.S. Pat. No. 5,051,562 to Bailey.
Cooking systems often have a temperature probe, a heating element, a temperature selector for enabling a user to select a desired cooking temperature, and control means for controlling the heating element(s) to be operated in different modes corresponding to the different stages of operation of the cooking system. For example, a deep fat fryer may be provided with a melt mode wherein solid shortening or liquid shortening below a predetermined temperature is heated at a slow rate, typically by pulsing the heating element, until the solid shortening melts or the liquid shortening reaches a predetermined temperature.
Numerous parameters may be input to a control system to control the cooking cycle of a food product or products. Some of these parameters are disclosed in U.S. Pat. No. 4,913,038 to Burkett et al., the disclosure of which is incorporated herein by reference. A single set of parameters may be input to control all cooking cycles performed by the cooking system, or unique sets of parameters may be input for each food product. Some of these parameters are described below.
Typically, after the shortening melts or reaches the predetermined temperature, the heating element will be operated in a second mode wherein the temperature of the shortening is rapidly increased to a selected temperature at which cooking is to occur. While a rapid increase in temperature to the selected temperature is desirable to minimize recovery time, if the temperature is raised too rapidly or turned off precisely at the selected temperature, or both, the internal heat capacity stored in the system may cause the temperature to exceed the selected temperature. This undesirable phenomenon is known as overshoot.
In order to prevent overshoot, some related art systems establish a temperature range, extending a predetermined number of degrees below the selected temperature, and operate the heating element in a full-on mode up to this temperature range and then operate the heating element in a reduced power or pulsed mode once the temperature is within the established temperature range. The rate of temperature increase is thereby more precisely regulated, and overshoot of the selected temperature is minimized. The effectiveness of providing such a temperature range is dependent in part upon the temperature at which this reduced power or pulsed mode initiates. A tradeoff occurs between how rapidly the selected temperature can be reached and how effectively overshoot is minimized.
One significant drawback with such an operating scheme is that the temperature range often is fixed and can not be altered by users for different food products. Under certain operating conditions, a user may desire a faster heating time and may be willing to tolerate some chance of overshoot. At other times, it may be desirable to forego the pulsed mode entirely and effectively provide thermostatic (on/off) control by setting the temperature range to zero. In yet other circumstances, the heating time is less important than assuring that overshoot is minimized, and a wider temperature range is preferable.
It, therefore, would be desirable to provide a control system capable of being operated in a full-on mode up to a first temperature and capable of being selectively operable in a pulsed mode thereafter to bring the temperature up to the selected temperature. A proportional control parameter determines the number of degrees, e.g., between 0 and 99, below the set temperature at which the pulsed mode will be initiated to avoid overshoot. This first temperature may be user selectable to provide more flexibility and enable a variety of user conditions to be taken into account to maximize food product cooking quality and consistency. For example, by selecting a first temperature near the set temperature, faster heating time can be obtained--that is the set temperature can be reached in a shorter period of time because the heating element remains in a full-on mode for a longer period of time. Conversely, in order to minimize the chance of overshooting the set temperature, the first temperature can be selected by the user to be substantially lower than the set temperature. Greater regulation of the shortening temperature can be obtained because the full-on mode of the heating element is terminated well below the set temperature. It would also be desirable to be able to effectively override the pulsed mode by providing a thermostatic (on/off) control, so that no pulsed mode occurs, thereby providing faster recovery time, but accepting maximum potential for overshoot. The present invention allows a proportional control parameter to be input for each of a plurality of food products or for a single parameter to be preprogrammed for all food products cooked in the cooking system.
In some related art systems that employ a pulsed mode as described above, the pulsed mode may be entered directly and immediately after the full-on mode. This, however, may also be a drawback because depending on operating conditions and system parameters, the pulsed mode might not be needed or desired. For example, if the temperature of the shortening is sufficiently close to the set temperature when the full-on mode is terminated, then the internal heat capacity of the cooking system may be capable of raising the shortening's temperature to the set temperature. This results from the temperature rise due to the stored internal heat capacity of the system after the heating element is turned off. This thermal lag time can cause the temperature of the shortening to drift up to the set temperature without the further application of heat, such as by pulsing the heating element. Other systems do not provide any pulsed mode, but rather calculate a temperature at which the heating element may be turned off, such that when the heating element is turned off, the internal heat of the system will cause the cooking medium to drift up to the set temperature. Precise control of the temperature of the cooking medium, however, is difficult to maintain in these systems.
It, therefore, would be desirable to cause a system to enter a wait or hold mode between the termination of a full-on mode and the initiation of the pulsed mode until a predetermined condition is met before any further control of the heating element is performed. This predetermined condition may be that the temperature rate of change is less than or equal to a predetermined value, such as the rate of change of temperature of the shortening within the fryer is less than or equal to a predetermined value, for example, zero. Once this predetermined condition is met, the wait or hold mode is exited and depending on the relationship between the temperature of the shortening and the set temperature when this mode is exited, the next mode of operation will be initiated. For example, if the temperature of the shortening is a predetermined number of degrees less than the set temperature when the predetermined condition is met, additional heat may be provided by again placing the heating element in a full-on mode.
Another important consideration when using a deep fat fryer for cooking is the proper maintenance of the cooking medium. Specifically, if shortening is used, it is necessary to filter the shortening periodically to maintain cooking quality due to the absorption of oils and odor from the cooked food products, and degradation of the shortening caused by breakdown thereof due to heat, extended use, and other factors. The number of times a type of food product may be cooked in the same shortening before filtering is required, i.e., the number of filter cycles or the filter cycle parameter, varies from one food product to another. For example, cooking french fries may not require the shortening to be filtered as often as is required with other products, such as breaded fish. In particular, it has been found that cooking breaded fish in a deep fat fryer requires the shortening to be filtered more frequently due to various factors, including the oil released by the fish during frying and the type of breading used. Other products, such as chicken, generally have filter cycles parameters somewhere between those of french fries and breaded fish.
Some related art systems provide an indication that it is time to filter the shortening based on a count of the number of cook cycles completed, regardless of the type of food product being cooked. This may lead to filtration that is either too frequent or too infrequent based on the types of food products cooked. It would, therefore, be desirable to provide an efficient and simple way to keep track of the number of times that different types of food products have been cooked and to provide an indication to the user when it is time to filter the cooking medium and thereby avoid under or over filtration of the cooking medium and further maintain the quality of the cooked product. The present invention allows the selection of a filter cycle parameter for each product or a single parameter for all products cooking in a single fryer.
Another concern related to deep fat fryer cooking operations is how to deal with the situation that arises when a temporary power outage condition causes an interruption of a cooking cycle. One answer would be to simply dispose of any food product that was being cooked when a power outage occurred. Obviously, this is not a desirable alternative because it wastes food products, which is neither socially nor economically desirable. It, therefore, would be desirable to allow a cooking cycle that was interrupted due to a temporary power outage condition to continue if the quality of the food product can be maintained. Further, this determination is important if the system is to keep track of the number of cooking cycles completed for each product.
In the present invention, the remaining cooking time and the temperature of the shortening at the time of power outage may be stored in a nonvolatile random access memory (NOVRAM). If the temperature of the shortening is a predetermined number of degrees below the set temperature when power is restored, the cook cycle may be aborted. If, however, the temperature of the shortening is less than a predetermined number of degrees below the set temperature when power is restored and a non-zero time is displayed for the remaining cooking time, the food cooking operation may continue from the point in the cook cycle at which the power outage occurred. It is advantageous to make a determination whether to abort or continue to cook based on how much the temperature has dropped. If the temperature has dropped too much, the food product may absorb too much shortening or it may take too long for the cooking medium to return to the set temperature whereby at the end of the cooking time the food product(s) may be of poor quality or not fully cooked. Alternatively, the determination may be based on the percentage of the cooking cycle completed when power is lost. The amount of time that elapses during the temporary power outage condition, however, may not be a reliable factor on which to base such a determination because the rate at which the temperature may drop may vary.
Typically, the introduction of a food product or products into a cooking medium causes the temperature of the cooking medium to drop. This phenomenon is sometimes referred to as "thermal shock." Usually, this temperature drop is not detected by the system immediately, so that there is a time delay between the temperature drop due to thermal shock and the system's recognition of and response to the need for additional heat. Some related art systems overcome this temperature drop by turning on a heating element or elements before the need for heat is realized by the system, thereby "anticipating" the need for heat. It would, however, be desirable to allow a user the flexibility of selecting whether or not to use such a load anticipation feature with each type of food product by programming a load anticipation parameter, e.g., an estimated temperature increase to offset the expected temperature drop due to the addition of a predetermined quantity of a food product, into each food product cooking cycle. Moreover, it would be a desirable safety feature to limit the temperature which the shortening can reach while using the load anticipation feature.
Some related art systems also cause the heating element to be controlled in an idle mode when a certain period of inactivity exists. This mode causes the cooking medium to be maintained at a temperature significantly below the set temperature to avoid unnecessary breakdown of the cooking medium while assuring that a cooking medium, such as shortening, remains in a liquid state and at a temperature that will enable satisfactory recovery time if the medium needs to be reheated to the set temperature for cooking. Nevertheless, it would be desirable to provide a user with the option of selecting when and how the idle mode should be entered. Typically, an idle mode may be activated automatically or manually. In the automatic setting, the idle mode might be activated if no cooking cycle was begun for a predetermined period of time. A single idle temperature may be set for all food products.
In view of the large number and variety of parameters involved in the cooking cycle for any food product, the variety of food products, and effect that any change in parameters may have on the quality of the cooked food products, it would be desirable to limit access to the control system program at various levels. This would permit various decision makers to alter the control system program, but each within only a circumscribed range of options. For example, this allows an operator to use the system within the scope of his or her authority, but also allows a manager to maintain hierarchical control of the system, facility, or plant. Thus, it might be desirable to allow different degrees of access to a cooking system operator, a restaurant manager, and a supervisor or diagnostic technician to ensure the reliable and efficient operation of the cooking system.
It would further be desirable to enable a computer controlled cooking system to store usage information, so that a user may be provided with an indication of the number of times a particular cycle has been completed and the total number of times that all of the cycles have been completed.